The escalating requirements for lubricants used in compression cylinders associated with the dynamic sealing of ethylene within the compressor cylinder and the hydraulic fatigue of pressure containing components subjected to cyclic pressures is considered one of the most demanding aspects of high-pressure manufacture of polyethylene. These aspects are discussed in more detail in Lubrication Engineering, Volume 37, 4, 203-208 (1981). High demands for large scale production require increasingly improved lubricants. This objective becomes particularly difficult to achieve given the sophisticated and capital-intensive nature of the process and challenges the limitations of polyethylene manufacture. Thus, the combined requirements of high-pressure equipment and cylinder life pose a challenge which, to date, has not been satisfactorily achieved.
U.S. Pat. No. 4,654,154 to Wilkelski discloses a conventional method of reducing cylinder gas leakage from compressors used in high pressure olefin polymerization processes wherein from about 3 to about 10 wt % of an antioxidant is added to the lubricating fluid provided to a compressor cylinder. Wilkelski discloses that the problem of increased gas leakage is due to an oxidation reaction occurring in the narrow annular passageway between the plunger and the cylinder packing.
The oxidation can take place due to the presence of unreacted peroxide initiators in the recycled ethylene and/or the introduction of a polymerization initiator, that is, oxygen gas to the ethylene before compression. The unwanted oxidation leads to undesirable consequences including buildup of excessive heat, high pressures and resultant high mechanical stress.
Despite the benefits achieved by the Wilkelski method, the provision of the additional antioxidant forces the cost of practicing the method upwards, thereby adversely affecting the commercial viability of the process.
There exists a need to provide an efficient and cost-effective technique to satisfy the demands of high-pressure polyolefin manufacture.